When a battery serving as a DC power source is reversely connected to a power conversion device such as a motor inverter device provided in a vehicle for example, a high current may flow in a parasitic diode of a MOSFET constituting the inverter. In this case, because of a heat dissipation structure of the MOSFET, it may resist heat in a short period of time but may be destroyed when time passes.
In view of this, there is a conventional product employing a structure in which, at a power-input-terminal portion, a series circuit of a Zener diode and a fuse is connected in parallel to an overvoltage protection diode so that the fuse can be fused. This makes it possible to determine the occurrence of reverse battery connection based on a fused state of the fuse.
Discussion on the above background art will be given. The below discussion may not necessarily constitute the prior art.
In the conventional product, the Zener diode itself needs to have a large rating in order that, until fusing of the fuse substituted by a bonding wire, the Zener diode is prevented from breaking down. Accordingly, an area occupied by the Zener diode becomes large when the Zener diode is formed on an IC, causing an increase in chip area in total.
In addition, although it is determinable whether a reverse voltage was applied based on presence or absence of fusing of the fuse, further information is unobtainable. For example, information such as a period of time until the fusing, voltage and temperature during the reversely connected state is unobtainable, and accordingly, it is unclear what happened until the fusing of the fuse, and a disadvantage is that useful information for failure diagnosis cannot be provided.